Nonhalogenated Solvent-Processed Thick-Film Ternary Nonfullerene Organic Solar Cells with Power Conversion Efficiency >13% Enabled by a New Wide-Bandgap Polymer

Although several donor polymers have been synthesized for use in nonfullerene organic solar cells (NFOSCs), the number of efficient p-conjugated donor polymers compatible with nonhalogenated solvent-processed thick active layer NFOSCs is limited. Two wide-bandgap p-conjugated donor polymers functionalized with a siloxane side chain, P1 (chlorine-free) and P2 (chlorinated), are designed and synthesized. The siloxane-functionalized side chains and/or Cl pconjugated donor polymers increase the absorption coefficients, reduce the energy losses, increase the charge-carrier mobility, and suppress the bimolecular recombination, which are beneficial to achieve high-performance thick- film ternary NFOSCs. Toluene-processed devices based on P2:IT-4F:BTP-4Cl, and P2: IT-4F:BTP-4F exhibit high power conversion efficiencies (PCEs) of 13.25% and 11.02% with fill factors (FFs) of 70.03% and 71.60%, respectively. A P2:IT-4F binary NFOSC exhibits a PCE of 10.38% with an FF of 69.78%, lower than that of the ternary NFOSC. The ternary device PCE of 13.25% is achieved using a 300 nm-thick active layer, indicating that the siloxane- functionalized side-chain pconjugated polymer easily controls the bulk heterojunction blend film thickness of the NFOSC. The findings may potentially aid the development of nonhalogenated solvent-processed thick-film ternary NFOSCs that can satisfy future production requirements.

Automated summary

Two wide-bandgap p-conjugated donor polymers with siloxane side chains were designed and synthesized for nonfullerene organic solar cells. The devices based on these polymers exhibited high power conversion efficiencies and fill factors, showing potential for future production needs.